Level and Loudness Meters

Level and Loudness Meters

Prism provides two complementary meters. VU Meter follows program level with an adjustable calibration reference. Loudness Meter reports perceived loudness over standard LUFS time windows. Both also provide faster level, peak, and stereo-correlation context.

Neither meter changes gain or limiting. To adjust the level seen by every Prism analyzer, use Input Trim.

VU Meter

VU movement is deliberately slower than a digital sample-peak display. It is useful for judging musical movement, sustained level, balance, and gain staging around a chosen reference.

Bar and needle layouts

• Bar can be Horizontal or Vertical.
• Needle can show separate Stereo needles or a Combined reading.

The default is a horizontal Bar display. Switching layout changes presentation, not the measured audio.

Reference level

The reference maps 0 VU to a chosen digital level. Prism includes:

Preset	0 VU reference	Typical context
K-20	-20 dBFS	SMPTE/film-style headroom
K-18	-18 dBFS	EBU/broadcast-style alignment
K-14	-14 dBFS	Streaming and general music; Prism default
K-12	-12 dBFS	Modern music
K-10	-10 dBFS	Louder masters
K-6	-6 dBFS	Hot or legacy alignment

You can also set a custom reference from -30 to 0 dBFS in 0.5 dB steps. Resetting a custom reference returns it to Prism's default -14 dBFS.

A reading above 0 VU does not automatically mean digital clipping. It means the slower program measurement is above the selected alignment point. Confirm headroom with the peak marks.

Additional indicators

The VU display includes fast left/right level context, peak marks, and a correlation bar. These help distinguish slow program movement from short peaks and stereo behavior.

Loudness Meter

Prism's Loudness Meter uses ITU-R BS.1770-style loudness measurement and lets the main readout follow one of three windows:

Readout	Meaning	Useful for
Momentary	The shortest loudness window	Immediate events and rapid changes
Short-term	A several-second view	Comparing phrases and sections; Prism default
Integrated	Accumulated program loudness	Overall loudness across the measured session

The selected value appears as the primary LUFS readout and bar. The display also includes fast stereo level/peak bars and correlation so transient headroom and channel behavior remain visible.

The meter shows a -14 LUFS target line as a convenient reference, not a rule or automatic normalization target. Delivery requirements vary by platform, broadcaster, project, and workflow.

Integrated measurement

Integrated LUFS accumulates over time. Silence, pauses, and program changes can affect what the final value represents, so begin a fresh analyzer session when starting a new comparison.

• In the desktop app, Stop Capture and then Start Capture from the tray, or start a newly selected source.
• In the Terminal UI, press r.
• In a DAW, reload or recreate the plugin instance according to the host's normal workflow; stopping transport alone does not necessarily reset it.

Correlation

Both meter modules show stereo correlation:

• toward +1: left and right are strongly similar;
• around 0: little linear relationship;
• below 0: opposing components may cancel when summed to mono.

Correlation is contextual. Wide ambience and effects can legitimately lower it. Sustained negative readings are a reason to inspect Vectorscope and listen in mono, not an automatic failure.

Choosing the right reading

• Use VU for slower musical movement around a working reference.
• Use peak indicators for digital headroom and brief events.
• Use Momentary LUFS for immediate loudness changes.
• Use Short-term LUFS to compare phrases or song sections.
• Use Integrated LUFS for a complete, consistently measured program.

Do not compare Integrated values unless the measurement boundaries are comparable. A full song, a chorus, and a few seconds of playback answer different questions.